Neural Circuits:

Wiring and

Tuning

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Synaptic Tuning

Three specific concepts associated with synaptic tuning:

v Long-Term Potentiation (LTP)

v Long-Term Depression (LTD)

v Spike-Timing Dependent Plasticity (STP)

Source

LTP:

v High-frequency presynaptic stimulation, or

v Low-frequency stimulation with postsynaptic depolarisation.

LTD:

v Low frequency stimulation

v Decrease in synaptic efficacy.

Significance

Definition

of STDP

Hardware Implementation of

STDP Example

“Neurons that fire together

wire together.”

v Hebb’s Law

Synaptic Wiring

v Topographic Maps

Map Development

Mechanisms

v Chemospecific matching:

• Similarity between input

neurons (or output) is

encoded by similarities

expressed with a molecular

gradient.

v Based off of Sperry’s

Chemoaffinity Hypothesis

Map Development Mechanisms

vActivity-dependent matching:

• Similarity is encoded by correlations in activity

Ø Coactive = more similar

How Does This Information

Affect Our Model?

v Our model:

• Activity-dependent

• Focuses on one

neuron at a time.

Short vs. Long-Distance

Guidance

Long-Distance:

v Chemotaxis mechanisms

v Structural type mechanisms

Short-Distance:

v Similar to our model

Conclusion

v How do we fine tune the strength of our current model?

1. Axonal Guidance

2. Strengthening/weakening of individual synapses based on relative

timing of pre/postsynaptic timing.